The circulatory responses to pregnancy, high-output cardiac failure and cirrhosis are characterized by vasodilation-mediated arterial underfilling. The present study will examine the effect of normalizing the hyperdynamic circulation in these states by inhibiting nitric oxide synthase (NOS) with or without cyclooxygenase inhibition. The non- osmotic arginine vasopressin (AVP) stimulation of aquaporin-2 (AQP-2) and resultant water retention with inhibition. Renin-angiotensin- aldosterone and Na retention with NOS inhibition will also be examined. Since a rise in neuronal NOS (nNOS) has been found in several organs in pregnancy, it is possible that increased nNOS in the effect of nNOS inhibition on GFR and the integrity of the TG feedback mechanism will therefore be examined. The further study of the role of specific NOS isoforms in pregnancy will be examined in pregnant eNOS, nNOS and iNOS knockout mice as compared to wild-type pregnant mice. The results of these studies will provide background information for future of understanding pre-eclampsia. Studies will also examine the effect of V2 AVP antagonist on AQP-2 water channels and water retention in rats with an aortocaval fistula and high output cardiac failure. The role of NO and prostaglandins in the arterial underfilling and any resultant effect on vasopressin-mediated AQP-2 water channels will be examined with NOS and cyclooxygenase inhibitors. The role of ANP and proximal tubule fluid reabsorption in high-output cardiac failure will also be studied using ANP and AQP-1 knockout mice, and ANP receptor antagonists. NO inhibition with L-NAME exerts a profound effect in reversing Na and water retention and ascites formation in cirrhotic rats. While the role of eNOS and iNOS have been studied from a molecular standpoint, a potential role of nNOS in cirrhosis has not been examined. Selective nNOS inhibitor will therefore be used in cirrhotic rats to examine the effects on systemic and renal hemodynamics, hormonal profile, as well as Na and water retention and ascites formation. The role of vasodilator peptides which enhance NO activity and are increased in cirrhosis (substance P, calcitonin gene-related peptide, and bradykinin) will be examined using cyclooxygenase inhibition. Several studies will be undertaken in knockout mice with cirrhosis to examine 1) the effect of specific NOS isoforms (eNOS, nNOS and iNOS knockout mice), 2) ANP (ANP knockout mice), and 3) proximal fluid reabsorption (AQP-1 knockout mice). In summary, the results of these studies will advance our knowledge of the important clinical states of pregnancy, cardiac failure nd cirrhosis. It is such experimental studies which have led to ongoing clinical investigations in patients using aquaretic agents (V2 vasopressin antagonist) in cardiac failure in cirrhosis.